Method of making transfer sheets and resulting article



METHOD OF MAKING TRANSFER SHEETS AND RESULTING ARTICLE Filed Deo. 12',1958 United States Patent O "ice METHOD F MAKING TRANSFER SHEETS ANDRESULTING ARTICLE George Cordery Phillpotts, Kingston Hill, Surrey,England, assignor to Caribonum Limited, Leyton, London, England, aBritish company Application December 12, 1958, Serial No. 779,892

Claims priority, application Great Britain August 14, 1956 Claims. (Cl.117-36) This application is a continuation-in-part of my applicationSerial No. 673,013, tiled July 19, 1957.

The present invention relates to manifolding and is concerned withimprovements in manifolding paper, and transfer sheet material ingeneral, which is of the substantially colourless type.

Manifolding papers are known wherein each sheet of paper has upon itsunderside an active coating containing a colourless, colour-developingsubstance. For copying purposes, this is placed upon another sheet ofpaper on the upper side of which is a reactive receptive coating, theactive and reactive receptive coatings being such that substantiallycolourless material is transferred from the active coating and thereupondevelops a contrasting mark on the reactive receptive coating. Areasonable multiplicity of copies, say six, may be obtained by using apack of such sheets and this is also the case where the rst sheet iscoated upon the underside only and for convenience is known as an Asheet, the next live sheets are coated upon the upper face with areactive receptive coating and upon the under face with an activecoating and are known as B sheets, and the nal sheet is coated, upon itsupper face only, with a reactive receptive coating and is known as a Csheet.

It has been proposed to coat the active sheet with small globulesconsisting of an outer skin of, for example, gelatin which has beensuitably hardened with formaldehyde and, within this hardened outerskin, a small quantity of an oily material containing a colourdevelopingsubstance, as for example methyl violet lactone and/orbenzoyl-leuco-methylene blue. These globules are mixed with a smallquantity of a binding substance in water and coated on paper. When thepaper so coated is brought face to face with a sheet of paper having anacid clay coated thereon, such for example as attapnlgite, and iswritten upon, the methyl violet lactone produces an immediate blue markwhich subsequently fades, while the benzoyl-leuco-rnethylene blue slowlydevelops a greenish-blue colour, by what is believed to be some form ofoxidation reaction. Thus, a copy is made which, starting blue, nallybecomes green or bluish-green. The process of making the globulesreferred to above is somewhat costly; this process is referred to inUnited States specifications Nos. 2,712,507 and 2,730,457 and also inBritish specification No. 751,600.

In co-pending application No. 647,684, filed March 21, 1957, in thenames of the applicant herein and D. J. Neale, it has been proposed toemulsify a solution of one or more substituted rnonoor di-leucauraminesin oil substances, disperse this solution in suitable binding material,as for example gelatin or ammonium alginate, and coat this dispersion onpaper with or without the addition to the emulsion of substances such astitanium White and/ or zinc oxide, but with a small quantity of analkaline substance such as sodium carbonate. A suitable reactivereceptive coating may be prepared, for example, from dextrin, blancfixe, phosphotungstic acid ,Y 2,885,302 Patented May 5, 1959 and/ortannic acid dissolved in dibfutyl tartrate, all of which in suitableproportions are dissolved or suspended in water, coated on paper anddried, a suitable coated weight after drying being 7.5 grams per squaremetre. When such an active sheet is brought into contact with thereactive receptive coating on another sheet, and written upon, animmediate dense blue writing is produced which does not fade. It isfoimd however, that it is difficult to prevent such sheets from markingspontaneously if such sheets are prepared in packs in the form of A, Band C sheets, unlessa subsequent process is used such for example asspraying the surface of the active sheet with a solution of for exampledexnin or gum arabic in water in such a way as to leave minute globulesupon the surface so that they prevent the two surfaces from coming intocontact unless pressure, such as might be caused by writing instrumentssuch as pencil, pen or typewriter, is brought to bear.

Accordingly, it is an object of the present invention to providetransfer sheet material, and a method for making it, which is notsubject to this disadvantage. A further object of the invention is toprovide a manifolding pack of two or more sheets of transfer material,which can be used to produce copies upon each sheet in the pack by theaction of Writing upon the uppermost sheet thereof.

According to the invention, transfer sheet material for use inmanifolding comprises a base web and a substantially colourless coatingcarried upon a surface of the base web, the coating being constituted bya continuous phase and a discontinuous phase, the discontinuous phase ofthe coating comprising a plurality of discrete particles ofpressure-responsive sponge-like material having a particle size fromabout 3 to about 10 microns, and the sponge-like particles havingabsorbed therein a colourforming fluid material containing a colourlessderivative of a `dyestuf adapted to be converted into the correspondingcoloured dyestuft on reaction with an acid substance, the continuousphase of the coating consisting of a dry and hard but pervious lmsuciently friable to permit the colour-forming fluid material to passtherethrough, the pressure responsive, sponge-like particles beingadapted normally to retain the colour-forming iluid material but topermit it to be expressed through the friable film, when the transfersheet material is subjected to writing pressure, and thereby to betransferred to a copy sheet in contact with the coated surface of thetransfer sheet material.

The invention also consists in a manifolding pack which comprises atleast two portions of transfer sheet material, each portion comprising asheet of paper, at least all sheets except the lowermost sheet in themanifolding pack carrying on the lower surface thereof a substantiallycolourless coating, the coating being constituted by a continuous phaseand a discontinuous phase, the discontinuous phase of the coatingcomprising a plurality of discrete spray-dried particles of apressure-responsive sponge-like material selected from the groupconsisting of alginates, casein and gelatin and having a particle sizefrom about 3 to about 10 microns, and the spongelike particles havingabsorbed therein an oily, colour-forming iluid material containing acolourless dyestutf derivative selected from the group consisting ofleucauramines and substituted leucauramines, the continuous phase of thecoating consisting of a dry and hard but pervious film sufficientlyfriable to permit the colour-forming fluid material to passtherethrough, and at least all sheets except the uppermost sheet in themanifolding pack carrying on the upper surface thereof a coatingincluding an acid substance, the colourless dyestulf derivativecontained in the colourforming fluid material being adapted to beconverted into the corresponding coloured dyestuif on reaction with theacid substance present in' the coating on the upper surface of the nextunderlying sheet of paper in the manifolding pack, thepressure-responsive sponge-like particles being adapted normally toretain the colour-forming fluid material but to permit the fluidmaterial to be expressed through the friable film when the manifoldingpack is subjected to writing pressure and thereby to be transferred tothe aforesaid next underlying sheet of paper and to react there with theacid substance to form the coloured dyestuff in the form of visiblewritten characters.

A further aspect of the invention comprises a method of making transfersheet material, which comprises the steps of providing a base web,forming a substantially colourless emulsion comprising a colourlessdyestuff derivative and a material adapted to form pressure-responsive,discrete sponge-like particles on spray-drying the emulsion,spray-drying the emulsion in the presence of a hardening agent to form aplurality of discrete particles of pressure-responsive sponge-likematerial having a particle size from about 3 to about l0 microns, theparticles having absorbed therein a colour-forming fluid materialcontaining the colourless dyestuff derivative, which is adapted to beconverted into the corresponding coloured dyestuf on reaction with anacid substance, dispersing the particles in a binder therefor to form adispersion having the binder as its continuous phase and the particlesas its discontinuous phase and coating the dispersion on to one surfaceof the base web thereby to form a coating in which the hinder forms adry and hard but pervious film Sulliciently friable to permit thecolour-forming fluid material to pass therethrough and thepressure-responsive spongelike particles are adapted normally to retainthe colourforming fluid material but to permit it to be expressedthrough the friable film when the transfer sheet material is subjectedto writing pressure and transferred to a copy sheet in contact with thecoated surface of the transfer sheet material.

It has been found that if the active emulsions, that is to say theemulsion containing leucauramines or substituted leucauramines, whichmay consist of these colourdeveloping substances dissolved in oils oroily substances and emulsiiied in a solution of ammonium alginate orcasein or gelatin, are spray-dried in such a manner that they producedried particles of approximately 3-6 microns in diameter, then theparticles so produced do not consist of an outer shell of gelatin orcasein or alginate but are of the character of minute Sponges, retainingwithin the pores of the sponge the solution of the colour-developingsubstances.

If suitable means are taken to harden the continuous phase of theemulsion, namely the casein, gelatin or ammonium or other alginate, itis found that the dried continuous phase of these particles is in itselfinsoluble in water and the particles may then be readily dispersed in abinding agent as for example a solution of starch in water or casein inwater or gelatin in water or triethanolamine al-ginate in water andcoated upon the paper. The binding agent or binder must have theproperties required to form a continuous phase of a coating, when thedispersion of the particles and binder is coated upon the paper, inwhich coating the particles constitutes the continuous phase. If theproportion of dissolved binder is sutiiciently high but not too high,the sponge-like particles are bound in place and it is found that thereis no tendency whatever to mark the reactive sheet when the active andreactive sheets are placed in contiguity unless and until the fairlyconcentrated pressure of a writing instrument such for example as a pen,pencil or typewriter is brought into use.

In hardening the base material of these particles, the normallywell-known materials are not in all cases satisfactory; thus for exampleit is unsatisfactory to add formaldeyde to the Igelatin or caseinsolutions, since hardening takes place before the material can bespraydried. If, however, the emulsions are pumped to the spray-drier bymeans of proportioning pumps so thatl the formaldehyde is added to thecasein or gelatin emulsions immediately before spray-drying, then thedesired hardening takes place. Since, in the process of spray-drying,considerable heat is used for drying the particles, some of theformaldehyde is lost by evaporation, but enough remains to harden theparticles to the desired extent. A satisfactory proportion offormaldehyde to be added to the emulsion in this way is 1000 partsemulsion to l part 40% formaldehyde solution, and for convenience thismay first be diluted with water to l0 parts. The ammonium alginate maybe caused to become insoluble in water by adding to an ammoniacalammonium alginate emulsion a small percentage of zinc oxide. This selvesnot only to render the spray-dried alignate powder insoluble in waterbut also to assist in whitening the emulsion. Spray-dried powderproduced in this way from ammonium alginate is soluble in medium tostrongly alkaline solutions, and these should be avoided whenconsidering the choice of binder for coating the powder on to paper.

Even under the best spray-drying conditions, it is found that particlesize varies fairly widely between rather less than 3 and rather morethan l0 microns, though the bulk of the particles so obtained can bemade between 3 and 6 microns. The large particles, however, tend to forma rather gritty coating on the paper or tend to be gritty here andthere, and the coating process may be rendered more satisfactory in thefollowing way.

The dried, hardened particles are dispersed as by Vigorous stirring in asuitable binder dissolved or mixed in water, as for example gelatin Vorammonium `alginate or, in the case of casein prepared particles orgelatin prepared particles, gelatin or casein only. The amount of binderto particles, while not critical, appears to be of some importance andseems to be between 0.15 and 0.4 for a good grade of gelatin.

This dispersion is then passed through a simple colloid .mill of thekind which has two disc-like faces in juxtaposition and a fewthousandths of an inch apart but with the faces moving at high speedwith respect to each other, as for example might be obtained `byrotating a disc l0 in diameter `at about 6500 r.p.m. situated 2 to3/1000 away from ya similar stationary disc into the centre of which thedispersion is fed. The dispersion passes between the stationary androtating discs in such a way that the grosser particles tend either tobe retained within the mill or to pass with the liquid layer through themill and thereby become reduced to an average size of approximately 3-6microns.

This dispersion is then coated and dried by heat on paper which may, ifdesired, have been prooed with a thin alkaline layer of ammoniumalginate in water or gelatin in water or casein in water. In the ease ofthe ammonium alginate, a little zinc oxide is added to ensureinsolubility when dry and in the case of casein and/or gelatin a littlehexamethylenetetramine is added. During the drying process wherein heatis used, the hexamethylenetetramine generates within the mixture alittle formaldehyde which then hardens the whole layer.

In the drying of the coating of the dispersion, the binder forming itscontinuous phase takes the form of a dry and hard lm, which isnevertheless pervious to fluid material and is suiciently friable topermit the colour-forming fluid material contained in the porouspressure-responsive sponge-like partie es to pass through such film,when the paper or other base web carrying the dried coating of thedispersion is subjected to writing pressure. In this way, thecolour-forming fluid matcrial may be transferred to the surface ofanother sheet of paper which is in contact with the dispersion coating'when the sheet carrying the latter is subjected to thc writingpressure. The presence of an acid substance in a coating ou thecontacting surface of the underlying sheet causes the colourlessdyestuff derivative in the fluid material expressed from the particlesand passed through the pervious film to be converted to the coloureddyestuff, :so that the written characters made on the upper sheet whenthe latter is subjected to the writing pressure appear in copy form onthe underlying, acid-coated sheet.

Any convenient method of coating these dispersions of sponge-likeparticles may be used, e.g. by means of rollers, doctor blades, airknives, or printing methods and the coated emulsion may then be dried bymeans of hot rollers, infra-red lamps or heaters with or without astrong blast of air either warm or cold.

EXAMPLE I Spray-dried emulsion An emulsion was made from the following:

Pts. by wt. Ammonium alginate (Collatex AX/RE)l 28 Finely-divided zincoxide powder 41/2 Water 500 0.880 ammonia solution 50 1Ohtainah1e fromAlginate Industries Ltd., Girvan, Scotland.

When the above had gone into a clear, pale brownish solution, thefollowing solution was emnlsitied in:

Pts. by wt. Sextol phthalate 30 Dibutyl phthalate 30p-Xylyl-leucauramine 3 The emulsiflcationwas continued until theoil-particles Were of the order of 5 microns in diameter, or less. Theemulsion was then spray-dried, to give particles of 5-15 microns indiameter.

EXAMPLE II Spray-dried emulsion The following were prepared:

Pts. Iby wt. Sextol phthalate 20 Dibutyl phthalate 2OPhenyl-leucauramine 2 The emulsion was spray-dried to give particles upto 20 microns in diameter.

EXAMPLE III Binding solution The powder prepared in Example I was mixedwith the following binder, passed through a high speed colloid mill toreduce the particle size to the order of 3-10 microns in diameter, andthe resulting dispersion was coated on to s paper to give a coatedweight of 4 lbs. per Double Crown ream (10 gms. per square metre).

Pts. by wt. Silver Stream gelatin 2 Titanium dioxide 21/2 Water 33Fixanol C, 1% soln. 3 5% sodium carbonate solution 2 Spray-driedalginate colour-developing solution powder 12 EXAMPLE IV v Bindingsolution The spray-dried powder prepared as in Example II was mixed witha binder as follows:

Pts. by wt. Titanium dioxide 5 Potato starch 15 Cold water 50 40%formaldehyde solution 'l Boiling water 250 Anhydrous sodium carbonate 4The titanium dioxide paste (I) was poured into the sodium carbonatesolution (II) and when the starch had gelatinised the following wasstirred in and the resultant dispersion passed through a high speedcolloid mill arranged to reduce the particles to diameters in the rangeof 3-10 microns, the bulk of the particles having diameters of 3-6microns:

Pts. by wt. Fixanol C, 1% solution 200 Spray-dried powder as in Ex. II65 EXAMPLE V Acid coating mixture Pts. by wt.v Dextrin 40 Blanc xe 1150Water 800 Pectin (240 grade)1 28 30% Fixanol C paste 15 1 Obtainablefrom British Drug Houses, Poole, Dorset.

Pts. by wt. Tannic acid 115 Dibutyl tartrate Finally, a solution of 16parts by weight of phosphotungstic acid was stirred in. The compositionwas coated on to paper to give a coating of 5 lb. per Double Crown rearn(1l-l2 gms. per sq. metre).

In order that the inventiony may be readily understandable to Ithoseskilled in the art, reference is made to the accompanying drawing inwhich:

Fig. 1 is a diagrammatic cross-section on an enlarged scale of one`formt of transfer sheet material;

Fig. 2 is a diagrammatic cross-section on an enlarged scale of one formof manifolding pack.

Fig. 1 shows a sheet of paper 10 carrying on a lsurface thereof a thinalkaline prooing layer 12. Over this layer 12, there is provided acoating comprising a continuous binder phase 14 and a discontinuousphase 16. The discontinuous phase 16 comprises a plurality of discrete,pressure-responsive, spray-dried sponge-like particles, which range'inparticlesize from 3 microns to l0 microns, the bulk ofthe particlesbeing between 3 and 6 microns in particle size. The particles haveabsorbed therein a colour-forming fluid material of the kind previouslydescribed in detail. The continuous binder phase 14 comprises a dry andhard but pervious film which is sufficiently friable to permit thecolour-forming fluid material in the particles 16 to pass through thefilm or binder phase 14, when Writing pressure is applied to the sheetof Fig. l to express the fluid material from the particles 16.

Fig. 2 shows a manifolding pack comprising an uppermost, or A sheet,three intermediate, or B, sheets and a lowermost, or C, sheet. The Asheet is similar to the sheet illustrated in Fig. l. Each of the Bsheets comprises a sheet of paper 18 carrying on the underside analkaline proofing layer 12 and a coating of particles 16 in a binder 14,as does the sheet illustrated in Fig. l. The B Sheets also carry, on theupper side, a coating 20 of an acid substance, e.g. tannic acid. The Csheet comprises a sheet of paper 22 carrying on the upper side an acidcoating 20 similar to that on the B sheets.

It may be mentioned that other forms of manifolding pack can be madewith the transfer sheet material of the invention. For example, the packcan consist exclusively of B sheets, one A sheet and one or more Bsheets or one or more B sheets and one C sheet.

I claim:

l. Transfer sheet material for use in manifolding, which comprises abase web and a substantially colourless coating carried upon a surfaceof the base web, the coating being constituted by a continuous phase anda discontinuous phase, the discontinuous phase of the coating comprisinga plurality of discrete particles of pressureresponsive sponge-likematerial having a particle size from about 3 to about l0 microns, andthe sponge-like particles having absorbed therein a colour-forming fluidmaterial containing a colourless derivative of a dyestuf adapted to beconverted into the corresponding coloured dyestuff on reaction with anacid substance, the continuous phase of the coating consisting of a dryand hard but pervious film :sufficiently friable to permit thecolour-forming fiuid material to pass therethrough, thepressure-responsive, sponge-like particles being adapted normally toretain the colour-forming fluid material but to permit it to beexpressed through the friable film, when the transfer sheet material issubjected to writing pressure, and thereby to be transferred to a copysheet in contact with the coated surface of the transfer sheet material.

2. Transfer sheet material for use in manifolding in contact With a copysheet, which transfer sheet material comprises a base web and asubstantially colourless coating carried upon a surface of the base Web,the coating being constituted by a continuous phase and a discontinuousphase, the discontinuous phase of the coating comprising a plurality ofdiscrete spray-dried particles of pressure-responsive sponge-likematerial having a particle size substantially within the range of fromabout 3 to about 6 microns, and the sponge-like particles havingabsorbed therein a colour-forming fiuid material containing a colourlessderivative of a dyestuff adapted to be converted into the correspondingcoloured dyestuff on reaction with an acid substance carried by the copysheet, the continuous phase of the coating consisting of a dry and hardbut pervious film sufiiciently friable to permit the colour-formingfluid material to pass therethrough. the pressure-responsive sponge-likeparticles being adapted normally to retain the colour-forming fluidmaterial but to permit it to be expressed through the friable film whenthe transfer sheet material is subjected to Writing pressure, andthereby to be transferred to the copy sheet in contact with the coatedsurface of the transfer sheet material.

3. Transfer sheet material for use in manifolding in contact with a copysheet, which transfer sheet material comprises a base web and asubstantially colourless coating carried upon a surface of the base web,the coating being constituted by a continuous phase and a discontinuousphase, the discontinuous phase of the coating comprising a plurality ofdiscrete spray-dried particles of pressure-responsive sponge-likematerial selected from the group consisting of alginates, casein andgelatin and having a particle size from about 3 to about 10 microns, andthe sponge-like particles having absorbed therein a colour-forming fluidmaterial containing a colourless derivative of a dyestuff adapted to beconverted into the corresponding coloured dyestuff on reaction with anacid substance carried by the copy sheet, the continuous phase of thecoating consisting of a dry and hard but pervious film suficientlyfriable to permit the colour-forming fiuid material tcI passtherethrough, the pressure-responsive sponge-like particles beingadapted normally to retain the colour-forming fiuid material but topermit it to be expressed through the friable film, when the transfersheet material is subjected to writing pressure, and thereby to betransferred. to the copy sheet in contact with the coated surface of thetransfer sheet material.

4. Transfer sheet material according to claim 3, Wherein the bulk of thesponge-like particles in the coating have a particle size from about 3to about 6 microns.

5. Transfer sheet material for use in manifolding, which comprises abase web and a substantially colourless coating carried upon a surfaceof the base web, the coating being constituted by a continuous phase anda discontinuous phase, the discontinuous phase of the coating comprisinga plurality of discrete water-insoluble particles of pressure-responsivesponge-like material formed by spray-drying a solution of a materialselected from the group consisting of alginates, casein and gelatin inthe presence of a hardening agent comprising formaldehyde, the particlesof sponge-like material having a particle size from about 3 to about 10microns, and the spongelike particles having absorbed therein acolour-forming fluid material containing a colourless derivative of adyestut adapted to be converted into the corresponding coloured dyestuffon reaction with an acid substance, the continuous phase of the coatingconsisting of a dry and hard but pervious film sufiiciently friable topermit the colour-forming fluid material to pass therethrough, thepressure-responsive sponge-like particles being adapted normally toretain the colour-forming fluid material but to permit it to beexpressed through the friable film, when the transfer sheet material issubjected to writing pressure, and thereby to be transferred to a copysheet in contact with the coated surface of the transfer sheet material.

6. Transfer sheet material for use in manifolding, which comprises abase web and a substantially colourless coating carried upon a surfaceof the base web, the coating being constiulted by a continuous phase anda discontinuous phase, the discontinuous phase of the coating comprisinga plurality of discrete particles of pressure-responsive sponge-likematerial having a particle size from about 3 to about 10 microns, andthe spongelike particles having absorbed therein a colour-forming fluidmaterial containing a colourless dyestuf derivative selected from thegroup consisting of leucauramine and substituted leucauramines andadapted to be converted into the corresponding coloured dyestuff onreaction with an acid substance, the continuous phase of the coatingconsisting of a dry and hard but pervious film sufiiciently friable topermit the colour-forming fiuid material to pass therethrough, thepressure-responsive sponge-like particles being adapted normally toretain the colour-forming fluid material but to permit it to beexpressed through the friable film, when the transfer sheet material issubjected to Writing pressure, and thereby to be transferred to a copysheet in Contact with the coated surface of the transfer sheet material.

7. Transfer sheet material for use in manifolding, in contact with acopy sheet which carries a coating comprising an acid substance, whichtransfer sheet material comprises a base Web and a substantiallycolourless coating carried upon a surface of the base web, the coatingbeing constituted by a continuous phase and a discon- 9 tinuous phase,the discontinuous phase of the coating comprising a plurality ofdiscrete water-insoluble particles having a particle size substantiallywithin the range of from about 3 to about 6 microns and comprising apressure-responsive sponge-like material formed by spraydrying, in thepresence of a hardening agent comprising formaldehyde, an aqueoussolution containing a material selected from the group consisting ofalginates, casein and gelatin, the sponge-like particles having absorbedtherein an oily, colour-forming fluid material containing a colourlessdyestuif derivative selected from the group consisting of leucauraminesand substituted leucauramines and adapted to be converted into thecorresponding coloured dyestuff on reaction with the acid substance, thecontinuous phase of the coating consisting of a dry and hard butpervious lm suciently friable to permit the colour-forming iluidmaterial to pass therethrough, the pressure-responsive sponge-likeparticles being adapted normally to retain the colour-forming fluidmaterial but to permit the fluid material to be expressed through the`friable lm when the transfer sheet material is subjected to writingpressure, and .thereby to be transferred to the copy sheet in contactwith the coated surface of the transfer sheet material, the dyestuifderivative thereby reacting with the acid substance to form the coloureddyestuff in the form of Written characters upon the copy sheet.

8. Transfer sheet material for use in manifolding in contact with a copysheet comprising a further portion of the same transfer sheet material,which comprises a base web, a substantially colourless first coatingwhich includes an acid substance carried upon one surface of the baseweb and a substantially colourless second coating carried upon the othersurface of the base web, the second coating being constituted by 'acontinuous phase and a discontinuous phase, the discontinuous phase ofthe second coating comprising a plurality of discrete spray-driedparticles of pressure-responsive sponge-like material selected from thegroup consisting of alginates, casein and gelatin and having a particlesize from .about 3 to about l microns, and the sponge-like particleshaving absorbed therein a colour-forming fluid material containing acolourless derivative of a dyestuif adapted to be converted into thecorresponding coloured dyestui on reaction with the yacid substancecarried by the further portion of the transfer sheet material, thecontinuous phase of the second coating consisting of a dry and hard butpervious lm suciently friable to permit the colourforming uid materialto pass therethrough, the pressureresponsive sponge-like particles beingadapted normally to retain the colour-forming fluid material but topermit it to be expressed through the friable lm when the transfer sheetmaterial is subjected to Writing pressure, and thereby to be transferredto the acid-coated surface of the further portion of transfer sheetmaterial in contact with the second coating of the first-mentionedportion of transfer sheet material.

9. A manifolding pack which comprises at least two portions of transfersheet material, each portion cornprising a sheet of paper, at least allsheets except the lowermost sheet in the manifolding pack carrying onthe lower surface thereof a substantially colourless coating, thecoating being constituted by Ia continuous phase and a discontinuousphase, the discontinuous phase of the coating comprising a plurality ofdiscrete spray-dried particles of a pressure-responsive sponge-likematerial selected from the ygroup consisting of alginates, casein andgelatin and having a particle size from about 3 to about l0 microns, andthe sponge-like particles having absorbed therein :an oily,colour-forming uid material containing a colourless dyestut derivativeselected from the group consisting of leucauramines and substitutedleucauramines, the continuous phase of the coating consisting of a dryand hard but pervious iilm sufciently friable to permit thecolour-forming iluid material to pass therethrough, and at least allsheets except the uppermost 10 sheet in the manifolding pack carrying onthe upper surface thereof a coating including an. acid substance, thecolourless dyestui derivative contained in the colourforming fluidmaterial being adapted to be converted into the corresponding coloureddyestui on reaction with the acid substance present in the coating onthe upper surface of the next underlying sheet of paper inthe-manifolding pack, the pressure-responsive sponge-like particlesbeing adapted normally to retain the colour-forming fluid material butto permit the fluid material to be expressed through the friable lm whenthe manifolding pack is subjected to writing pressure and thereby to betransferred to the aforesaid next underlying sheet of paper and to reactthere with the acid substance to form the coloured dyestuif in the formof visible written characters.

10. A manifolding pack according to claim 9, wherein each sheet of papercarrying on the lower surface thereof the coating constituted by thecontinuous and discontinuous phases is provided between such coating andthe paper itself with an alkaline proofing layer which serves to preventstaining of the paper caused by undesired interaction of the dyestuffderivative and the acid substance.

11. A method of making transfer sheet material for use in manifolding,which comprises the steps of providing a base web, forming asubstantially colourless emulsion comprising a colourless dyestuiderivative and a material adapted to` form pressure-responsive, discretesponge-like particles on spray-drying the emulsion, spraydrying theemulsion in the presence of a hardening agent to form a plurality ofdiscrete particles of pressure-responsive sponge-like material having aparticle size from about 3 to about 10 microns, the particles havingabsorbed therein a colour-forming fluid material containing thecolourless dyestui derivative, which is adapted to be converted into thecorresponding coloured dyestui on reaction with an acid substance,dispersing the particles in a binder therefor to form a dispersionhaving the binder as its continuous phase and the particles as itsdiscontinuous phase and coating the dispersion on to one surface of thebase web thereby to form a coating in which the binder forms a dry andhard but pervious lm sufiiciently friable to permit the colour-formingfluid material to pass therethrough and the pressure-responsivesponge-like particles are adapted normally to retain the colour-formingfluid material but to permit it to be expressed through the friable lmwhen the transfer sheet material is subjected to writing pressure andtransferred to a copy sheet in contact with the coated surface of thetransfer sheet material.

l2. A method of making transfer sheet material for Iuse in manifolding,which comprises the steps of providing a base web, forming an emulsionof a substantially colourless dyestuif derivative selected from thegroup consisting of leucauramine and substituted leucauramines dissolvedin an oily substance with `a material selected from the group consistingof alginates, casein and gelatin, spraydrying the emulsion to form aplurality of discrete, pressure-responsive sponge-like particles of theselected material having a particle size from about 3 to about 10microns, the sponge-like particles having absorbed therein acolour-forming fluid material containing the colourless dyestuiderivative, dispersing the thus-formed particles in a binder to form acoatable dispersion of which the particles constitute the discontinuousphase and the binder constitutes the continuous phase, the continuousphase of the coating consisting of a dry and hard but pervious lm.sufficiently friable to permit the colour-forming uid material to passtherethrough, and coating the dispersion upon a surface of the base web,thereby to form a coating in which the pressure-responsive sponge-likeparticles are adapted normally to retain the colour-forming uid materialbut to permit it to be expressed through the friable film, when thetransfer sheet material is subjected to writing pressure, andtransferred to a copy sheet in contact with the coated surface of thetransfer sheet material, the colourless dyestuif derivative thereuponbeing converted into the corresponding coloured dyestuff on reactionwith an acid substance present on the contacting surface of the copysheet.

13. A method according to claim 11, whichV further comprises the step ofapplying' a'coating of the acid substance to the other surface of thebase web.

14. A method according to claim 12, which further comprises the step ofapplying a coating comprising tannic acid to the other surface of thebase web.

l5. A method of making a manifolding pack of transfer sheet material,Which comprises the steps of providing a base web, applying an alkalineproofing layer to a surface of the base web, forming a substantiallycolourless emulsion comprising a colourless dyestuf derivative selectedfrom the group consisting of leucauraniine and substituted leucauraminesdissolved in an oily substance with a material selected from the groupconsisting of yalginates, casein and gelatin, spray-drying the emulsionin the presence of a hardening agent comprising formaldehyde thereby toconvert the emulsion into a plurality of discrete, water-insoluble,pressure-responsive sponge-like particles of the selected materialhaving a particle size substantially within the range of from about 3 toabout 6 microns, the sponge-like particles having absorbed therein acolour-forming uid material containing the colourless dyestulfderivative, dispersing the thus-formed Huidliolding particles in abinder material to form a dispersion of which the spray-dried particlesconstitute the discontinuous phase and the binder material constitutesthe continuous phase, applying ya coating of the dispersion to a surfaceof the base webthereby to form a colourless coating in which thepressure-responsive sponge-like particles are contained ina dry and hardbut pervious film suciently friable to permit the colour-forming uidmaterial to pass therethrough and the particles are adapted normally toretain the colour-forming Huid material but to permit it to be expressedthrough the friable film, when the transfer sheet material is subjectedto Writing pressure, and transferred to a copy sheet in contact with thecoated surface of the transfer sheet material, applying to the othersurface of the base web from that having the coating of the dispersionthereon a colourless coating of a material comprising tannic acid, anddividing the thus-coated base web into sheets and stacking the sheetsinto a manifolding pack in which the colourless dyestuff derivativecarried in the coatingof the dispersion on cach sheet in the pack isadapted to be converted into the corresponding coloured dyestuff onreaction with the acid coating on the adjacent sheet in the pack.

References Cited in the tile of this patent UNLTED STATES PATENTS ivd-1-

1. TRANSFER SHEET MATERIAL FOR USE IN MANIFOLDING WHICH COMPRISES A BASEWEB AND A SUBSTANTIALLY COLOURLESS COATING CARRIED UPON A SURFACE OF THEBASE WEB, THE COATING BEING CONSTITUTED BY A CONTINUOUS PHASE OF THECOATING TINUOUS PHASE, THE DISCONTINUOUS PHASE OF THE COATING COMPRISINGA PLURALITY OF DISCRETE PARTICLES OF PRESSURERESPONSIVE SPONGE-LIKEMATERIAL HAVING A PARTICLES ABOUT 3 TO ABOUT 10 MICRONS, AND THESPONGE-LIKE PARTICLES HAVING ABSORBED THEREIN A COLOUR-FORMING FLUIDMATERIAL CONTAINING A COLOURLESS DERIVATIVE OF A DYESTUFF ADAPTED ON BECONVERTED INTO THE CORRESPONDING COLOURED DYESTUFF ON REACTION WITH ANACID SUBSTANCE, THE CONTINUOUS PHASE OF THE COATING CONSISTING OF A DRYAND HARD BUT PREVIOUS FILM SUFFICIENTLY FRIABLE TO PERMIT THECOLOUR-FORMING FLUID MATERIAL TO PASS THERETHROUGH, THEPRESSURE-RESPONSIVE, SPONGE-LIKE PARTICLES BEING ADAPTED NORMALLY TORETAIN THE COLOUR-FORMING FLUID MATERIAL BUT TO PERMIT IT TO BEEXPRESSED THROUGH THE FRIABLE FILM, WHEN THE TRANSFER SHEET MATERIAL ISSUBJECTED TO WRITING PRESSURE, AND THEREBY TO BE TRANSFERRED TO A COPYSHEET IN CONTACT WITH THE COATED SURFACE OF THE SHEET MATERIAL.